[jessedhillon]

Capital One 360, formerly ING Direct, has nailed this on the sending side. The sender needs to know the recipient's email addr and the last four of their bank acct # -- the recipient will receive an email which takes them to a page where they enter the full account # and, if those match, money transferred.

[abawany]

SSN to receive money from Dwolla!? Holy cow. Yes, I like the ING solution very much as well though for repeated (but not recurring) transfers, the need to re-enter the bank account number gets a bit cumbersome.